The present invention relates to a photomask including a reticle, used in the manufacture of semiconductor devices.
In general, a photomask has a large number of high-resolution images. If a photomask has one or more defective images and is used in the manufacture of semiconductor devices, the manufacturing yield of semiconductor devices is reduced. Therefore, it is important to test the pattern of a photomask prior to the use thereof.
One conventional method for testing the pattern of a photomask is performed by determining whether or not a scanning signal obtained by scanning the pattern of the photomask is inconsistent with a reference scanning signal based on reference data stored in a storage unit such as a magnetic tape. In this case, the scanning of the pattern of a photomask is performed by moving the stage on which the photomask is mounted. Of course, it is necessary that the scanning signal obtained by scanning the pattern of the photomask be synchronized with the reference scanning signal read out of the magnetic tape. However, when the motion of the stage is reversed, it is difficult to synchronize the two scanning signals. The synchronization requires a highly accurate movement of the stage, thereby increasing the cost of a unit for testing a photomask.